Implementing Shared Content selector on MVC widgetCancel

I have an MVC widget where I would like to implement 'Shared Content' selector like the one in Content Block widget. I have added a Guid property on my controller but the widget designer from Sitefinity Thunder does not provide an interface for 'Shared Content' selector. How can I implement that on my widget?

I found this documentation ( http://www.sitefinity.com/documentation/documentationarticles/change-your-dynamic-content-selector-to-choose-from-generic-content )but when I implemented it, I don't see any content block listed even though I have created some. Below is the part on my designer that the documentation mentions to change. Any idea why this is not working?

It looks like that I have to put some text on the search box then it will show me some results. The problem is , what I see is 'undefined' as a title instead of an actual title. What needs to be changed to get the title show up properly?

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